CHEMISORBED IMPURITIES AND HETEROGENEOUS NUCLEATION 
(mm) 
ai 
0.01 
VAPOR PRESSURE OF ETHYL AMINE 
° 
° 
2 
| | | 
0.0001 
“100 140 -180 
TEMPERATURE °c 
Fic. 5—Vapor pressure curve of ethyl 
amine 
temperature for the supercooled cloud are given 
for each series of measurements. The results, in 
terms of ice nucleation temperature for lead 
iodide as a function of cryostat temperature, are 
given in Figure 6 and the results in terms of ice 
nucleation temperature as a function of vapor 
pressure of ethyl amine are given in Figure 7. 
When one examines Figure 6, the curve for nu- 
cleation temperature as a function of eryostat 
temperature, it appears exponential. The plot of 
nucleating temperature as a function of log va- 
por pressure of ethyl amine, however, appears to 
be a straight line, indicating that the nucleating 
temperature bears the same relationship to va- 
por pressure of the ethyl amine as the vapor 
pressure has to the temperature of the ma- 
terial. 
An analysis of the data obtained in the static 
tests shows that the lower limit of measured 
change is a decrease in nucleation temperature 
from —6° to —13° when the partial pressure of 
ethyl amine was approximately 0.0004 mm. This 
corresponds to, at one atmosphere, one part of 
ethyl amine per two millon parts of air. Going up 
towards the higher partial pressures of nuclei 
poison, a partial pressure of 1.1 mm of amine will 
lower the freezing point of supercooled water 
to —33°, a change in nucleating temperature of 
27°. This latter pressure, however, is quite high; 
it corresponds to better than one part per thou- 
sand of ethyl amine and is unrealistic when one 
is thinking in terms of atmospheric contami- 
"Cc 
TEMPERATURE OF ICE NUCLEATION 
° 
[a | ta | WRN 
| 
-60 
-100 
-140 
CRYOSTAT TE 
MPERATURE °C 
Fic. 6—Inhibition of ice nucleation as a 
function of cryostat temperature 
(mm) 
TUTTI 
0.0iL 
VAPOR PRESSURE OF ETHYL AMINE 
°o 
8 
0000! 
| | 
iL 
10 
-20 -30 -40 
TEMPERATURE OF ICE NUCLEATION °C 
Fre. 7—Inhibition of ice nucleation as a 
function of ethyl amine vapor pressure 
TaBLE 1—Results of static runs 
249 
Cryostat Vapor pressure Nucleation 
temperature ethyl amine temperature 
2 mm BG 
—81 ileal —33.4 
—101 0.19 —28.2 
—120 0.033 —25 
—129 0.016 —22 
—139 0.006 —20 
—171 0.0004 —13.4 
